This invention relates to a precision balanced shaft and a method of balancing a shaft. The particular embodiment disclosed herein by way of illustration is a multi-plate rotatable cutter head, a pair of which are used to simultaneously from a tongue on one side of a flooring strip and a mating groove on the other side as the flooring strips pass between them. Commercial manufacture of flooring takes place at high speed and requires extreme precision since the assembled flooring strips must mate with essentially no cracks, spaces or gaps. It is therefore essential to use extremely sharp, well-balanced cutter plates. As used herein, the term "cutter plate" refers to a flat, circular disk with cutting teeth around the periphery and a center bore for being mounted onto a motor spindle. As described below, two or more stacked cutter plates with other assembly parts make up a "cutter head" assembly. A properly operating cutter head assembly as a unit must not only be as concentric as possible, but the blades must be concentric relative to each other and must be properly spaced from each other.
The principles of this invention have application in any environment where rapidly-rotating shafts must be precision balanced, for whatever reason. Other applications of this invention therefore include machine tool shafts, particularly numerically-controlled milling machines, lathes, drill presses and the like, wood-processing machines, such as lathes, drill presses, planers, joiners, sanders, shapers, routers, and saws, including circular saws, miter saws. Other applications include watercraft, and aircraft. Members which may be mounted on the shafts include cutter blades, sensors of various types, accessory attachments, cams and switches.
Insofar as the exemplary embodiment is concerned, a number of prior art cutter head assembly types and methods are known. In a prior art, a simple tapered, self-centering collet is used, onto which are stacked three rotatable cutter plates which collectively form the profile to be cut onto the edge of the flooring strip. Tightening the cutter plates onto the collet tends to reduce the concentricity of the assembly, such that the required balance and concentricity must be achieved by using ajoining stone which grinds the cutting edges of the cutter plates to compensate for the initial out-of-round condition. Still, eccentricity of 0.003-4 inches is the best that can ordinarily be achieved. Moreover, the requirement to grind away part of the cutting edges reduces the life of the cutter plates by one-half and requires that all of the cutter plates be replaced at the same time.
One attempted solution to this problem involves the use of a hydraulic pressure sleeve, such as made by ETP Transmission AB. The pressure sleeve is fitted onto the motor spindle, and has a central void which is pressurized with grease. The pressure sleeve expands towards the spindle and the blades. Since the pressure is exerted evenly onto all surfaces and in all directions, the sleeve is automatically centered.
However, this assembly technique does not center the blades themselves, nor does it balance the blades relative to each other. This is done with shims, since often the tolerances of the cutter plates are outside the range of pressure expansion of the pressure sleeve.
The requirement to use shims to space the blades has been eliminated by using intermediate spacing plates and nuts to correct the distance between cutter plates on the pressure sleeve as wear occurs. This type of assembly also eliminates the need to join the cutting teeth, thus providing a longer life to the cutter plates. However, there are also disadvantages to this technique, including the requirement that the entire assembly must be removed from the motor spindle for adjustment. It is therefore difficult to maintain concentricity while making adjustments to the cutter plate spacing. In addition, sawdust tends to become trapped between the cutter plates, making adjustment within the environment of a wood flooring plant difficult. The invention disclosed in this application solves these problems by utilizing two separate pressure sleeves performing different functions.